Conventional, hot melt adhesive dispensing valve assemblies are of course well-known in the art. One example of a pneumatically-controlled hot melt adhesive dispensing valve assembly is disclosed within U.S. Pat. No. 6,315,168 which issued to Bolyard, Jr. et al. on Nov. 13, 2001. While this dispensing valve assembly is quite satisfactory from an operational point of view, a special sealing cartridge for the hot melt adhesive and control air fluids is required. In addition, the control valve assembly requires special maintenance procedures to be implemented, and the overall assembly is noisy. Electromagnetic solenoid-controlled dispensing valve assemblies are in fact also known in the art, however, they suffer from several different operational drawbacks. For example, one type of conventional electromagnetic solenoid-controlled dispensing valve assembly comprises the use of a single electromagnetic solenoid assembly for moving the dispensing valve assembly from its seated or CLOSED position to its unseated or OPENED position, while a coil spring mechanism is utilized to move the dispensing valve assembly from its unseated or OPENED position back to its seated or CLOSED position. As can readily be appreciated, however, the use of the coil spring mechanism as the sole means for achieving the return stroke or movement of the dispensing valve assembly from its unseated or OPENED position back to its seated or CLOSED position is problematic for several reasons.
For example, in order to ensure that the movement of the dispensing valve assembly from its unseated or OPENED position back to its seated or CLOSED position is in fact achieved in a relatively quick and responsive manner in order to, in turn, ensure that the discharge or dispensing of the hot melt adhesive material, from the nozzle portion operatively associated with the dispensing valve assembly, is terminated at a substantially precise point in time and without exhibiting stringing of the hot melt adhesive material, the biasing force of the coil spring mechanism must necessarily be significant or substantially large. Conversely, however, if the coil spring mechanism does in fact have a significantly large biasing force oriented in the valve seating or CLOSED direction, then the stroke or movement of the dispensing valve assembly will be relatively slow in that the movement or stroke of the dispensing valve assembly must overcome the significantly large biasing force of the coil spring mechanism. Alternatively, the single electromagnetic solenoid assembly must be fabricated so as to be relatively large in size in order to generate a sufficiently large electromagnetic force which can easily, readily, and quickly overcome the aforenoted substantially large biasing force of the coil spring mechanism in order to ensure the precise and rapid stroke or movement of the valve stem, and the ball valve mounted thereon, when the ball valve is to be moved from its seated or CLOSED position to its unseated or OPENED position.
A need therefore exists in the art for a new and improved solenoid-actuated hot melt adhesive or other thermoplastic material dispensing valve assembly wherein the operational drawbacks characteristic of the conventional, prior art solenoid-actuated hot melt adhesive dispensing valve assemblies can effectively be overcome. More particularly, a need exists in the art for a new and improved solenoid-actuated hot melt adhesive dispensing valve assembly wherein the movements or strokes of the valve stem and the ball valve mounted thereon, from the seated or CLOSED position to the unseated or OPENED position, as well as from the unseated or OPENED position to the seated or CLOSED position, can be assuredly and quickly achieved without the need for a relatively large coil spring mechanism for generating a relatively large valve closure biasing force, and without the need for a relatively large electromagnetic solenoid assembly for generating a relatively large valve opening force for effectively overcoming the relatively large valve closure biasing force of the relatively large coil spring mechanism.